Tools and machine elements of various kinds are used in a wide range of industries such as manufacturing, pulp, forest and steel industries as well as in different vehicle and defense applications.
Tool materials are usually divided into two groups depending on field of use; material for cutting and material for plastic and punching machining. Of the two fields of use, cutting tools are faced with the highest demands, such as e.g. cutting edge materials. This field of use demands a material with high wear resistance in combination with high toughness at elevated temperatures to obtain as high abrasion resistance as possible for a tool, i.e. high resistance towards abrasive wear.
Known tool materials are inter alia tool-steel, high-speed-steel and various cemented carbides. Tool-steel is used for simple hand held tools were only a good edge sharpness is required since the tool-steel requires low temperatures and reasonable forces during use.
High-speed-steel is alloyed steel with fairly high contents of carbon, chromium and wolfram, molybdenum and vanadium and in some cases even cobalt. High-speed-steel has high wear resistance while maintaining high hardness up to approximately 500° C., depending on the amounts of vanadium and wolfram.
Cemented carbides are the most common tool material because of the low production costs and are primarily made of wolfram carbide bonded together by cobalt. By varying the proportions of the constituents cemented carbides with material properties suitable for different areas of application can be obtained. By coating the cemented carbide with e.g. titanium carbide the wear resistance and therefore the tool life can be increased. Attempts to coat cemented carbides with a thin layer of synthetic diamond have also been made. To increase the properties of cemented carbides a material called cermets has been developed, a material with nickel instead of cobalt and titanium carbide or titanium-carbon-nitride instead of wolfram carbide. Cutting tools used for metal cutting have an optimal life span of 12-13 minutes, after which the wear mechanisms affect the cutting process and tolerances. The cemented carbide product can thereby be considered to have served its time. Wear mechanisms that affect the life span of a cutting edge are e.g. flank wear and chipping or nicking. Flank wear is a continuous loss of tool material through abrasive and adhesive wear. Chipping or nicking is a crack formation with subsequent fracture of the cutting edge.
Various ceramic materials exist which have good wear resistance and strength at elevated temperatures but have the drawback that they are brittle.
Material wise it has been impossible to manufacture materials with both high wear resistance and combinations of hardness and toughness, hence, compromises have been made. In simple applications the geometrical shape of the tool may for instance be designed in such a way that the tool exhibits acceptable wear resistance and strength.
Previous attempts have been made to design wear a resistant material, like the one suggested by the present invention, in which wolfram and carbon have been added to a white iron alloy. These attempts have however failed on account of the fact that the right proportions between wolfram and carbon, which decides the final properties of the material, are very difficult to obtain. Wolfram as a raw material is also quite expensive, a fact that has limited the development.
A traditional approach for manufacturing tools or other equipment includes the following steps:
AlloyCastingPlastic machiningCuttingHardening+annealing GrindingFinished part
The Japanese-patent JP 2301539 discloses a method for manufacturing a Ni—Cr white iron comprising TiC and TiCN at which a material with high hardness and wear resistance is obtained.
In the European patent application EP 0 380 715 a composite material with high resistance to abrasive wear is disclosed. The composite material contains particles of cemented carbide, of which at least 70% have a grain size in the range of 2-15 mm, as well as white iron. The white iron alloy contains a complex carbide component to which an alloying element is added. Furthermore, the white iron alloy comprises 2.5 to 4.0% carbon and exhibits a Cr to C relation (Cr%/C%) in the range of 1-12. Furthermore, a way to produce the above mentioned composite is disclosed in the document, comprising the step of casting molten white iron around the cemented carbide particles.
In the U.S. Pat. No. 4,365,997 a compound material and a way to produce such a material is disclosed. The compound material contains a metal matrix, which includes cemented carbide grains with a size of between 0.1 mm and 5 mm. The metal matrix includes carbon, silicon, manganese, vanadium, chromium, wolfram, aluminum and iron. The cemented carbide comprises WC, W2C, TiC, TaC or a mixture of these materials. The method for producing the above mentioned compound material is to add grains of cemented carbide to the molten metal matrix. The grains are encapsulated in a polymer-based matrix, which evaporates when the grains are added to the molten metal matrix, and subsequently the molten material solidifies.
Patent application WO 94/11541 announces a method for the manufacture of engineering ferrous metals such as cast iron and steel, which method includes adding to a molten engineering ferrous metal modified carbide particles, in solid state, and thereafter allowing the ferrous metal to solidify. The carbide particles are modified in the sense that they are covered with e.g. iron or a ferrous alloy so that the modified carbide particles receive a density equal to or close to the density of the ferrous metal. This density matching results in a uniform distribution of the carbide particles in the ferrous metal melt.
The Japanese patent JP 59104262 discloses a composite material with an inner steel layer and an outer layer comprising cast iron in which wolfram carbide particles or similar hard carbide particles have been evenly distributed. Furthermore, a method for producing such a material is disclosed. The method includes adding pre-heated carbide particles to molten cast iron and then casting the molten material around a pre-heated steel tube.
SE 185 935 relates to methods for alloying metal melts, predominantly including cast iron. In the document, an alloy, which can contain both chromium and wolfram, is mentioned, but nothing about any carbide structure.
EP 571 210 concerns the manufacture of a corrosion resistant alloy based on vanadium carbide. The material is created by e.g. the melting of a powder material.
SE 399 911 concerns the casting in of cemented carbide particles in iron based cast iron alloys. The suggested solutions is not intended to create melting and alloying, even though it is mentioned that alloys between the cast metal and the cemented carbide can occur and that these, generally speaking, are non advantageous. The patent does not describe the substitutional solution of wolfram in a chromium carbide structure.
DE 649 622 describes an alloy, which can contain both wolfram and chromium, but nothing of the interactions between the two during the formation of carbides.
GB 348 641 describes an alloy, which can contain both wolfram and chromium, but nothing of the interactions between the two during the formation of carbides.